Hormonal contraception is considered the most reliable method of reversible contraception today. It requires the continuous taking of pills, generally daily, regardless of the frequency of intercourses. For women with infrequent sexual intercourse, however, preparations that are dependent on coitus and thus can be taken less often, with reduced exposure to the effective ingredients, would be more advantageous. Although recognized for a long time (Canzler et al, Zbl. Gynäkol, 1984, 106:1182-1191), the need for such on-demand contraception remains unmet (Aitken et al, Contraception, 2008, 78-:S28-S35).
Women are actually creating such methods themselves out of existing products. In Ghana, a study conducted in 2003 reported that women were using norethindrone tablets, marketed for treatment of various gynecologic problems, as an “on demand” oral contraceptive. More recently, anecdotal reports and data collected by colleagues at Family Health International indicate that women in other parts of Africa and elsewhere are deliberately using emergency contraceptive pills in this manner.
Although oral methods do not provide protection against sexually transmitted infections, studies conducted several decades ago reported that various doses of levonorgestrel used as a regular postcoital contraceptive may provide protection with an efficacy comparable to the overall efficacy of condoms and other barrier methods in typical use (United Nations Development Programme/United Nations Population Fund/World Health Organization/World Bank Special Programme of Research, Development and Research Training in Human Reproduction, Task Force on Post-Ovulatory Methods of Fertility Regulation. Efficacy and side effects of immediate postcoital levonorgestrel used repeatedly for contraception. Contraception 2000; 61:303-8). It was further proposed to evaluate whether a single vaginal administration of levonorgestrel gel prior to intercourse would interfere with the ovulatory process. (Brache et al, Contraception, 2007; 76:111-116).
Other progestative agents have been used as post-coital emergency contraception. Emergency contraception (EC) refers to back-up methods for contraceptive emergencies which women can use within the first few days after unprotected intercourse to prevent an unwanted pregnancy. For instance the preclinical studies and the first clinical trials with ulipristal acetate, developed by HRA Pharma for emergency contraception, have proved that a single dose of 50 mg of ulipristal acetate is safe and efficacious when administered to women seeking emergency contraception within 72 hours after unprotected intercourse (Creinin et al, 2006, Obstetrics and Gynecology, 108(5):1089-1097).